Semiconductor device, structure and methods

ABSTRACT

A 3D semiconductor device, including: a first die including first transistors and first interconnect, overlaid by a second die including second transistors and second interconnect, where the first die has a first die area and the second die has a second die area, where the first die area is at least 10% larger than the second die area, and where the second die has a thickness of less than four microns.

This application claims benefit of provisional U.S. Patent ApplicationNo. 62/149,651, filed on Apr. 19, 2015. This application claims priorityto the foregoing application. The contents of the foregoing applicationare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates to the general field of Integrated Circuit (IC)devices, fabrication methods, and die bonding and die stacking devicesand methods, and more particularly to multilayer or Three DimensionalIntegrated Circuit (3D-IC) devices, fabrication methods, and die bondingand die stacking devices and methods.

2. Discussion of Background Art

Over the past 40 years, there has been a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling”; i.e., component sizeswithin ICs have been reduced (“scaled”) with every successive generationof technology. There are two main classes of components in ComplementaryMetal Oxide Semiconductor (CMOS) ICs, namely transistors and wires. With“scaling”, transistor performance and density typically improve and thishas contributed to the previously-mentioned increases in IC performanceand functionality. However, wires (interconnects) that connect togethertransistors degrade in performance with “scaling”. The situation todayis that wires dominate the performance, functionality and powerconsumption of ICs.

3D stacking of semiconductor devices or chips is one avenue to tacklethe wire issues. By arranging transistors in 3 dimensions instead of 2dimensions (as was the case in the 1990s), the transistors in ICs can beplaced closer to each other. This reduces wire lengths and keeps wiringdelay low.

There are many techniques to construct 3D stacked integrated circuits orchips including:

-   -   Through-silicon via (TSV) technology: Multiple layers of        transistors (with or without wiring levels) can be constructed        separately. Following this, they can be bonded to each other and        connected to each other with through-silicon vias (TSVs).    -   Monolithic 3D technology: With this approach, multiple layers of        transistors and wires can be monolithically constructed. Some        monolithic 3D and 3DIC approaches are described in U.S. Pat.        Nos. 8,273,610, 8,557,632, 8,298,875, 8,642,416, 8,362,482,        8,378,715, 8,379,458, 8,450,804, 8,574,929, 8,581,349,        8,642,416, 8,687,399, 8,742,476, 8,674,470, 8,803,206,        8,902,663, 8,994,404, 9,021,414, 9,023,688, 9,030,858,        9,117,749, 9,219,005; U.S. patent publication 2011/0092030; and        U.S. Patent Applications, 62/077,280, 62/042,229, Ser. Nos.        13/803,437, 61/932,617, 14/607,077, 14/642,724, 62/139,636,        62/149,651, 62/198,126, and 62/239,931. The entire contents of        the foregoing patents, publications, and applications are        incorporated herein by reference.

Electro-Optics: There is also work done for integrated monolithic 3Dincluding layers of different crystals, such as U.S. Pat. No. 8,283,215,U.S. Pat. Nos. 8,163,581, 8,753,913, 8,823,122, 9,197,804; and U.S.patent application Ser. No. 14/461,539. The entire contents of theforegoing patents, publications, and applications are incorporatedherein by reference.

An early work on monolithic 3D was presented in U.S. Pat. No. 7,052,941and follow-on work in related patents includes U.S. Pat. No. 7,470,598.A technique which has been used over the last 20 years to build SOIwafers, called “Smart-Cut” or “Ion-Cut”, was presented in U.S. Pat. No.7,470,598 as one of the options to perform layer transfer for theformation of a monolithic 3D device. Yet in a related patent disclosure,by the same inventor of U.S. Pat. No. 7,470,598, U.S. application Ser.No. 12/618,542 it states: “In one embodiment of the previous art,exfoliating implant method in which ion-implanting Hydrogen into thewafer surface is known. But this exfoliating implant method can destroylattice structure of the doped layer 400 by heavy ion-implanting. Inthis case, to recover the destroyed lattice structure, a long timethermal treatment in very high temperature is required. This longtime/high temperature thermal treatment can severely deform the celldevices of the lower region.” Moreover, in U.S. application Ser. No.12/635,496 by the same inventor is stated: [0034] Among the technologiesto form the detaching layer, one of the well known technologies isHydrogen Exfoliating Implant. This method has a critical disadvantagewhich can destroy lattice structures of the substrate because it useshigh amount of ion implantation. In order to recover the destroyedlattice structures, the substrate should be cured by heat treatment invery high temperature long time. This kind of high temperature heattreatment can damage cell devices in the lower regions.” Furthermore, inU.S. application Ser. No. 13/175,652 it is stated: “Among thetechnologies to form the detaching layer 207, one technology is calledas exfoliating implant in which gas phase ions such as hydrogen isimplanted to form the detaching layer, but in this technology, thecrystal lattice structure of the multiple doped layers 201, 203, 205 canbe damaged. In order to recover the crystal lattice damage, a thermaltreatment under very high temperature and longtime should be performed,and this can strongly damage the cell devices underneath.” In fact theInventor had posted a video infomercial on his corporate website, andwas up-loaded on YouTube on Jun. 1, 2011, clearly stating in referenceto the Smart Cut process: “The wafer bonding and detaching method iswell-known SOI or Semiconductor-On-Insulator technology. Compared toconventional bulk semiconductor substrates, SOI has been introduced toincrease transistor performance. However, it is not designed for 3D ICeither. Let me explain the reasons . . . . The dose of hydrogen is toohigh and, therefore, semiconductor crystalline lattices are demolishedby the hydrogen ion bombardment during the hydrogen ion implantation.Therefore, typically annealing at more than 1,100 Celsius is requiredfor curing the lattice damage after wafer detaching. Such hightemperature processing certainly destroys underlying devices andinterconnect layers. Without high temperature annealing, the transferredlayer should be the same as a highly defective amorphous layer. It seemsthat there is no way to cure the lattice damage at low temperatures.BeSang has disruptive 3D layer formation technology and it enablesformation of defect-free single crystalline semiconductor layer at lowtemperatures . . . ”.

In at least one embodiment presented herein, at least one innovativemethod and device structure to repair the crystal lattice damage causedby the hydrogen implant is described.

Regardless of the technique used to construct 3D stacked integratedcircuits or chips, heat removal is a serious issue for this technology.For example, when a layer of circuits with power density P is stackedatop another layer with power density P, the net power density is 2P.Removing the heat produced due to this power density is a significantchallenge. In addition, many heat producing regions in 3D stackedintegrated circuits or chips have a high thermal resistance to the heatsink, and this makes heat removal even more difficult.

Several solutions have been proposed to tackle this issue of heatremoval in 3D stacked integrated circuits and chips. These are describedin the following paragraphs.

Publications have suggested passing liquid coolant through multipledevice layers of a 3D-IC to remove heat. This is described in“Microchannel Cooled 3D Integrated Systems”, Proc. Intl. InterconnectTechnology Conference, 2008 by D. C. Sekar, et al., and “ForcedConvective Interlayer Cooling in Vertically Integrated Packages,” Proc.Intersoc. Conference on Thermal Management (ITHERM), 2008 by T.Brunschweiler, et al. and “High Performance Heat Sinking for VLSI,” IEEEElectron Device Letters, vol. EDL-2, No. 5, May 1981, by D. B. Tuckermanand R. F. W. Pease.

Thermal vias have been suggested as techniques to transfer heat fromstacked device layers to the heat sink. Use of power and ground vias forthermal conduction in 3D-ICs has also been suggested. These techniquesare described in “Allocating Power Ground Vias in 3D ICs forSimultaneous Power and Thermal Integrity” ACM Transactions on DesignAutomation of Electronic Systems (TODAES), May 2009 by Hao Yu, Joanna Hoand Lei He.

In addition, thermal limitations during IC fabrication have been a bigobstacle on the road to monolithic three-dimensional ICs. Thesemiconductor and microelectronic processing techniques to formtransistors, circuits, and devices, for example to form some siliconoxides or nitrides, repair damages from processes such as etching andion-implantation, annealing and activation of ion implanted species, andepitaxial regrow techniques, have processing temperatures (for example,greater than 400° C.) and times at temperature that would damage andharm the underlying metallization and/or device layers and structures.These processes may involve transient (short timescales, such as lessthan 500 ns short wavelength laser pulses) heat exposures to the waferbeing processed, or steady state applications (such as RTA, RTO, spike,flash, CVD, ALD) of heat and/or heated material or gases that may haveprocessing times of seconds, minutes, or hours.

Techniques to remove heat from 3D Integrated Circuits and Chips andprotect sensitive metallization and circuit elements from either theheat of processing of the 3D layers or the operationally generated heatfrom an active circuit, will be beneficial.

There are many advantages to constructing a 3D IC system using die towafer integration, such as, for example, as presented in U.S. patentapplication Ser. No. 14/642,724 with respect to at least FIGS. 44A-B andFIGS. 45A-C. A severe limitation in respect to such die to waferintegration is the throughput of such processing and its implication onthe end 3D device cost. Herein we seek to present alternative processflows to support higher throughput and lower cost for such die to waferintegration including processes to allow ultra-thin die which furtherreduces cost and increases integration.

Additionally the 3D technology according to some embodiments of theinvention may enable some very innovative IC devices alternatives withreduced development costs, novel and simpler process flows, increasedyield, and other illustrative benefits.

SUMMARY

The invention may be directed to multilayer or Three DimensionalIntegrated Circuit (3D IC) devices, fabrication methods, and die bondingand die stacking devices and methods.

In one aspect, a 3D semiconductor device, comprising: a first diecomprising first transistors and first interconnect, overlaid by asecond die comprising second transistors and second interconnect,wherein said first die has a first die area and said second die has asecond die area, wherein said first die area is at least 10% larger thansaid second die area, and wherein said second die has a thickness ofless than four microns.

In another aspect, a 3D semiconductor device, comprising: a first diecomprising first transistors and first interconnect, overlaid by asecond die comprising second transistors and second interconnect,wherein said first die is sourced from a first wafer with a diametergreater than 280 mm and said second die is sourced from a second waferwith a diameter less than 240 mm, and wherein said second die has athickness of less than four microns.

In another aspect, a 3D semiconductor device, comprising: a first diecomprising first transistors and first interconnect, overlaid by asecond die comprising second transistors and second interconnect,wherein said second die comprises at least two alignment markspositioned close to said second die edge, and wherein said second diehas a thickness of less than four microns.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIGS. 1A and 1B are exemplary illustrations of a processed wafer;

FIG. 1C is an exemplary illustration of a processed wafer with an addedlayer;

FIGS. 2A-2E are exemplary illustrations of a process flow for die towafer manufacturing;

FIG. 3 is an exemplary illustration of an exemplary processed wafer withstreets;

FIG. 4 is an exemplary illustration of an exemplary 4 dice with streetsand alignment marks/structures; and

FIGS. 5A and 5B are exemplary illustrations of a 3D semiconductordevice.

DETAILED DESCRIPTION

An embodiment of the invention is now described with reference to thedrawing figures. Persons of ordinary skill in the art will appreciatethat the description and figures illustrate rather than limit theinvention and that in general the figures are not drawn to scale forclarity of presentation. Such skilled persons will also realize thatmany more embodiments are possible by applying the inventive principlescontained herein and that such embodiments fall within the scope of theinvention which is not to be limited except by the appended claims.

Some drawing figures may describe process flows for building devices ordie bonding and die stacking devices and methods. The process flows,which may be a sequence of steps for building a device or die bondingand die stacking devices and methods, may have many structures, numeralsand labels that may be common between two or more adjacent steps. Insuch cases, some labels, numerals and structures used for a certainstep's figure may have been described in the previous steps' figures.

There are many advantages to constructing a 3D IC system using die towafer integration. A severe limitation in respect to such die to waferintegration is the throughput of such processing and its implication onthe end 3D device cost. Herein we seek to present alternative processflows to support higher throughput and lower cost for such die to waferintegration including processes to allow ultra-thin die which furtherreduces cost and increases integration.

It is known in the art that die to wafer processing could be done withdies having thickness of less than about 20 micron to about a diethickness of about 6 micron. Such has been presented in a paper byChristine Harendt, Evangelos A. Angelopoulos, Stefan Endler, Mahadi-UlHassan, Tu Hoang, Joachim N. Burghartz, “Mechanical Stability ofUltra-thin Chips down to 6 μm,” in Forum ‘be-flexible’ 2010, 11thInternational Workshop, Munich, Germany, (Vortrag), Vorträge nur fürTeilnehmer, Dec. 1, 2010 (2010); and a paper by Saleh Ferwana, et al.,“Self-Aligned Through Silicon Vias in Ultra-Thin Chips for3D-Integration,” Proc. of 4th Electronics System Integration TechnologyConferences (ESTC), Amsterdam, Netherlands, (Vortrag), 2012, bothincorporated herein by reference. As well, in the book Ultra-thin ChipTechnology and Applications, Joachim N. Burghartz, ed. Berlin, Germany:Springer, December, 2010, ISBN: 978-1-4419-7275-0, p. 467 (2010),incorporated herein by reference. Additionally, in U.S. Pat. Nos.8,466,037 and 7,951,691, both incorporated herein by reference.

As illustrated in FIG. 1A, a wafer, such as a silicon substrate, may beprocessed to support a die to wafer 3D process flow. Using processesdescribed in U.S. patent application Ser. No. 14/642,724, in at leastFIGS. 22-24, a base wafer 110 may be processed to construct a top highquality epitaxial layer 116 for future device layers on top of arelatively thick low porosity layer 114. Low porosity layer 114 may haveless than 50% porous structure and even about 20% porosity and wouldhave thickness of less than 20 micron or even with die thickness ofabout 6 micron. Underneath low porosity layer 114 a high porosity layer112 may be constructed to support future ‘cut’ or ‘cleave’ for a layertransfer as was previously presented in at least U.S. patent applicationSer. No. 14/642,724. Epitaxial layer 116 could be grown to a few nmthick layer, for example, such as 5 nm or 10 nm, to a moderately thicklayer, such as, for example, 100 nm or 200 nm, to a relatively thicklayer, such as, for example, 1 micron, or 3 microns thick.

The low porosity layer 114 could be partially oxidized to give itstronger mechanical strength. For example, dry oxidation of the poroussilicon may be carried out at a low temperature of about 400° C. Thisresults in oxidization of about 1˜3 nm of the inner walls of the pores,thus preventing the structure of the porous silicon from changing undera subsequent high-temperature treatment.

As illustrated in FIG. 1B, the wafer of FIG. 1A may be processed toconstruct a full stratum of device layer 118 utilizing a portion of or asubstantial majority of epitaxial layer 116. Device layer 118 could havefull circuits including P type and N type transistors with their metallayers interconnection processed as known in semiconductor industryprocesses. Device layer 118 could include thru layer vias or preparatorystructures for TLVs, which may have diameters of less than about 1 um,less than about 400 nm, less than about 200 nm, or less than about 100nm. Processed wafer 120 could then be at least electrically andfunctionally tested (a die within processed wafer 120 may be said to be‘pretested’) and made ready for the following steps. Processed wafer 120may include device layer 118, low porosity layer 114, high porositylayer 112, and base wafer 110.

As illustrated in FIG. 1C, an additional embodiment is shown wherein asimilar base wafer structure as illustrated in FIG. 1A may be processedwith the addition of solid silicon layer 126. Solid silicon layer 126may be disposed between low porosity layer 114 and high porosity layer112. The structure of FIG. 1C could be fabricated using methods such asdescribed in U.S. patent application Ser. No. 14/642,724 such as inrespect to at least FIG. 30D. Second porous layer 3024 may correspond tolow porosity layer 114, remaining monocrystalline layer 3022 maycorrespond to solid silicon layer 126, and cut double layer lower layerof porous silicon 3012 and upper layer of porous silicon 3014 maycorrespond to high porosity layer 112. Solid silicon layer 126 may havea thickness similar to layer epitaxial 116 and may have two mainfunctions. First, solid silicon layer 126 helps stabilize the structurelater-on as the structure is etched to allow pulling out of individualdies. And second it helps in providing a better interface to the pullingout apparatus which could use, for example, vacuum suction to providethe holding of the individual dies. The structure illustrated in FIG. 1Ccould be further processed to form a full stratum of device layer 118 asillustrated in FIG. 1B and so forth.

As illustrated in FIG. 2A, a customized carrier wafer 210 may bedesigned and formed to support the die being pulling out of, forexample, processed wafer 120. The customized carrier wafer 210 may beformed by etching die sized cavities 212 of about 1 micron depth (zdirection) into a substrate wafer 200. The die size (x and y direction)may be defined according to the size of the dies on processed wafer 120.In most cases the dies are rectangular shaped with lengths and widths ofa few mm up to about reticle size of 20×30 mm. As illustrated in FIG.2B, which is an enlargement of bubble 220 of FIG. 2A, streets 214 may bedisposed between the die sized cavities 212. Streets 214 could be fewmicrons in width up to about 100 micron in width. Substrate wafer 200may include a conventional monocrystalline silicon wafer, or may beformed from other materials, for example, such as aluminum, ceramic, andso on that may provide dimensional stability and bondability.

As illustrated in FIG. 2C, processed wafer 120 may be bonded ontocustomized carrier wafer 210 and may include alignment of streets 214 sothat the processed dies of processed wafer 120 may be floating over diesized cavities 212 of customized carrier wafer 210 while the boding maybe done at the streets of both wafers. The actual processed circuits ofdevice layer 118 are aligned to the die sized cavities 212 of thecustomized carrier wafer 210.

As illustrated in FIG. 2D, base wafer 110 of processed wafer 120 may becut-off or cleaved from the bonded structure utilizing the cut porouslayer high porosity layer 112.

As illustrated in FIG. 2E, structure 211 may be formed after cleaningthe porous cut residues and etching the streets 132 of the remainingportion of processed wafer 120, thus leaving the dies 230 almostfloating and lightly connected to the customized carrier wafer 210.Structure 211 may include custom carrier 210 with streets 214 lightlybonded to the edge of customized carrier wafer 120 dies 230. These dies230 would include functional circuits from device layer 118 and supportporous structure 114. Porous support structure 114 may have a thicknessof about 6 to 20 microns.

In general a 6-20 micron thick silicon-porous silicon structure would betransparent enough to enable good detection of the individual die (suchas dies 230) alignment marks for the following steps of precise diealignment. Alternatively the alignment marks could be exposed with anetch step. Selectivity for such a step would not be an issue as thealignment mark could be formed with metal layers while the 6-20 micronetch is of silicon and silicon oxide.

The dies 230 from the structure 211 could be pulled out for integrationinto a 3D IC structure. This step could be done one die at a time at arelatively slow throughput. An improved process was suggested in a papertitled “Simultaneous Cu—Cu and Compliant Dielectric Bonding for 3DStacking of ICs,” A. Jourdain et al, II TC07, and paper by A. Sigl etal, “Throughput Enhanced Flip-Chip to Wafer Bonding: The Advanced Chipto Wafer Bonding,” ECS09; both incorporated herein by reference. Theysuggested a modification of the bonding process into two steps, firsttacking the individual dies, and second, collectively bonding allstacked dies in a wafer-level bonding process. U.S. Pat. Nos. 8,597,980and 8,697,542, incorporated herein by reference, also teach two step dieto wafer bonding.

In a die to wafer bonding flow it could be desired to test the dies sothat only good dies get bonded and also the target base circuit could betested so bonding could be saved and be done to a good yielded circuitdie(s) on either or both.

The die tacking could be done, for example, by using a glue, temporarycopper to copper bonding or ultrasound techniques. Some glue wouldevaporate during the second step of the simultaneous bonding leaving noresidue. Some of the tacking techniques do form metal to metalconnection that would allow testing and rework to make sure all die totarget base circuit connections are good before moving to the longerprocess for simultaneous permanent bonding of all dies.

For the known processes for metal to metal, copper to copper bonding, ashort cycle of such processes could provide enough holding force to holdthe die once placed until all the dies are placed, and then continuewith the full permanent bonding performed for all dies on the wafersimultaneously. The short bonding/tacking should take less than a minuteas it is done a die at a time, the permanent bonding could take morethan 30 minutes as it is done to many dies such as full wafer populatedstructure simultaneously. Such bonding is presented in a paper by Y. H.Hu, et al., “Cu—Cu Hybrid Bonding as Option for 3D IC Stacking,” IEEEIITC 2012, incorporated herein by reference.

Tacking using glue has been presented in a paper by J. Van Olmen, etal., “3D Stacked IC demonstrator using Hybrid Collective Die-to-WaferBonding with copper Through Silicon Vias (TSV),” IEEE 3DIC 2009, and ina paper by A Jourdain, et al., “Mechanical and electricalcharacterization of BCB as a bond and seal material for cavities housing(RF-)MEMS devices,” J. Micromech. Microeng. 15 (2005), both incorporatedherein by reference.

Tacking could be done using ultrasound for bonding. Ultrasound could beuse for tacking and also for permanent bonding. Ultrasound bondingprocessing is presented in a paper by Yanhong Tian, “Investigation ofultrasonic copper wire wedge bonding on Au/Ni plated Cu substrates atambient temperature,” Journal of Materials Processing Technology (2008),incorporated herein by reference.

Equipment for picking a die and placing it on a wafer is available inthe market by multiple vendors such as the FC 300 by SET, and similarequipment by EV Group. Both companies support two step bonding as beendescribed herein.

These die bonders are designed to support fast placement of about 5-10micron alignment accuracy or slower placement with alignment accuracy ofabout 1 micron.

While 1 micron accuracy is good enough for TSV based 3D IC system, amuch higher precision would be desirable for monolithic 3D applicationsas been presented in U.S. patent application Ser. No. 14/642,724. Anembodiment for such monolithic 3D applications is a three phase die towafer bonding scheme.

The first step would be to lightly tack dies to the target wafer usingexisting die to wafer bonders such as the before mentioned FC 300. Suchplacement would be done with better than 10 micron accuracy.

The second step could use a precision die to wafer bonder to relocatethe dies that had been placed at 10 micron accuracy to better than about400 nm, or to better than about 100 nm, or better than about 50 nm, orbetter than about 10 nm. The step could be done following the completionof the above first step. This precise tacking could use a stronger typeof tacking than the first step. Following this stronger tacking secondstep a sub-step of testing and rework as needed could be done to supporta higher yielding process. The equipment for such small step of diesrealignment is not currently available as standard industry equipment. Aco-pending application details a possible construction of such precisehigh throughput die realignment equipment. This new type equipment wouldbe leveraging the pre-placement of dies at about 10 micron accuracy sothe realignment movement is for only about 10 micron or less, making iteasier to achieve 100 nm precision at the end of such small movement anddoing so at a good throughput.

For this second step of precise alignment of the individual dies, dielevel alignment could be used.

Once the second step is complete and all dies on the targetwafer/substrate are placed at the required precision such as 100 nm, andpossibly tested to validate good tacking connection, the third step ofsimultaneous bonding could commence.

In the third step all dies are permanently bonded at their preciseposition. Some bonding techniques would leverage the surface tension ofthe bonding surface to hold the dies at their precise location and toachieve a self-alignment to complete the third step of having all thedie precisely and permanently boded to the target wafer.

Once all die had been bonded the wafer could be moved to further theprocess of 3D integration. A follow-on step could etch the low porositylayer 114. The porous layer etch rate is about 100,000 faster than theetch rate of solid (substantially non-porous) silicon. Low porositylayer 114 could be removed completely leaving the thin active circuitsof device layer 118. Through layer vias could now be made to support thefollowing steps of the 3D integration.

When the starting material structure used is the one illustrated in FIG.1C, then the thinning process would start first by etching the top thinsolid silicon layer 126 and then thick low porosity layer 114.

As illustrated in FIG. 3, exemplary processed wafer 300 may includemultiple processed dies 302 and ‘dicing streets’ between dies such ashorizontal street 310 and vertical street 312. As presented before fordie to wafer bonding, the cutting of dies off exemplary processed wafer310 would be done by etching rather than saw dicing. The etch would berelatively shallow at about 6-20 micron depth as the layers of multipleprocessed dies 302 was already thinned by cutting off the base waferusing, for example, the porous cutting layer 112. A typical wafer iscircle (with or without a notch, etc.) with diameter size of about 150mm to 300 mm, but may be greater than 300 mm. Typical dies are arectangular size of 3×3 mm to 20×30 mm. Typical street widths are 50micron to 200 micron.

As illustrated in FIG. 4, exemplary 4 dies 402 with streets for‘dicing’/etching such as horizontal street 410 and vertical street 412,and exemplary die alignment marks/structures 420. Typical die alignmentmark/structure size could be 1-5 micron. The alignment area would besmall relevant to the die size area so this additional overhead costwould be very small. The die alignment marks/structures 420 could bepart of the metal layers of the active circuits of device layer 118within each die 402. The die alignment marks/structures 420 could beformed by multiple metal layers. The die alignment marks/structures 420could be formed close to the die edge 408, within about 20% of a dielength/width, within about 10% of a die length/width, within about 5% ofa die length/width.

The target wafer for which these dies would be precisely bonded to couldhave also die alignment marks. Those could be placed in the street areaas those streets would not be etched or diced prior to the precise diebonding of step 2, especially if the design is that the die bondingwould be toward the target bonding die edge. The target alignmentmarks/structures could correspond to the size of the die to be bonded ifthat die is smaller than the target die it is bonded to. If it isdesired to bond smaller die to a target die and not toward the edge ofthat target die than it could be desired to have the target diealignment marks/structures inside the target die.

The target wafer could be processed with patterns according to theplaned bonded dies so that all the areas which are not going to becovered with bonded dies would be protected from the planned diethinning etch step. Silicon nitride could be used for such or otherlayers with good etch selectivity to the underlying structure and tosilicon and silicon oxide which would be etched for the thinning step.

After the thinning step, an oxide deposition and CMP planarization couldbe used to form a flat top surface for the follow-on 3D integrationsteps.

FIG. 5A illustrates some of the advantages of die level bonding. FIG. 5Aillustrates a 3D semiconductor device 500 which includes a first die 502and a smaller (by area) second die 504, where the second die 504 isbonded and connected to first die 502. Second die 504 may be bonded andconnected to first die 502 utilizing the techniques and methods herein.Second die 504 may be electrically connected to first die 502 using thrulayer vias, such as is described herein and in the incorporatedreferences, and these thru layer vias may have diameters less than about1 um, or less than about 400 nm, or less than about 200 nm, or less thanabout 100 nm, or less than about 40 nm. The area of first die 502 may begreater than the area of second die 504 by a least about 5%, or by atleast about 10%, or buy at least about 25%, or by at least about 50%.Second die 504 may include alignment marks 520. FIG. 5A also illustratesa third die 506 bonded to the first die 502 and may be placed side byside to the second die 504 showing flexible heterogeneous integration ofa 3D device.

FIG. 5B illustrates a side view of FIG. 5A's top view of a 3Ddevice/system. While the first die 512 could have a thickness of 50micron or even the original thickness of the original wafer plusprocessing (for example, about 775 um for a 300 mm wafer) the uppersecond die 514 and third die 516 could have a thickness of less than 10micron or even thinner than 200 nm using the process described herein.

An advantage of the die level bonding is the flexibility with wafer sizeintegration. Most modern fabs currently use larger than 280 mm wafers,commonly known as 300 mm or 12 inch wafers. In most cases it would bevery hard to find a fab having a smaller wafer size being used foradvance process nodes such as 28 nm or more advanced. Likewise it isvery hard to find an old process nodes fab with 300 mm wafers. Old nodessuch as 250 nm or older use smaller than 240 mm wafer size such wafercommonly known as 200 mm or 8 inch wafers. Smaller wafer size are alsoused for non-digital CMOS such as RF, high power, electro-optics and soforth. Most of the wafers that are non-silicon are only available withsmaller than 240 mm wafer size. Die level 3D integration opens theability to form 3D device with mixed technologies and overcomes thediffering wafer diameter/size barrier.

An advantage of the die level bonding is the ability to pre-test the diebefore bonding and accordingly use what is commonly called Known GoodDies (“KGD”). In U.S. Pat. No. 914,255, incorporated herein byreference, a method for contact-less testing is described in referenceto FIG. 24A-C. Such testing could be advantageous for very thin diebonding method as has been described herein.

While concepts in this patent application have been described withrespect to 3D-ICs with two stacked device layers, those of ordinaryskill in the art will appreciate that it can be valid for 3D-ICs withmore than two stacked device layers. Additionally, some of the conceptsmay be applied to 2D ICs.

Some embodiments of the invention may include alternative techniques tobuild IC (Integrated Circuit) devices including techniques and methodsto construct 3D IC systems. Some embodiments of the invention may enabledevice solutions with far less power consumption than prior art. Thedevice solutions could be very useful for the growing application ofmobile electronic devices and mobile systems such as, for example,mobile phones, smart phone, and cameras, those mobile systems may alsoconnect to the internet. For example, incorporating the 3D ICsemiconductor devices according to some embodiments of the inventionwithin the mobile electronic devices and mobile systems could providesuperior mobile units that could operate much more efficiently and for amuch longer time than with prior art technology.

Smart mobile systems may be greatly enhanced by complex electronics at alimited power budget. The 3D technology described in the multipleembodiments of the invention would allow the construction of low powerhigh complexity mobile electronic systems. For example, it would bepossible to integrate into a small form function a complex logic circuitwith high density high speed memory utilizing some of the 3D DRAMembodiments of the invention and add some non-volatile 3D NAND chargetrap or RRAM described in some embodiments of the invention. Mobilesystem applications of the 3D IC technology described herein may befound at least in FIG. 156 of U.S. Pat. No. 8,273,610, the contents ofwhich are incorporated by reference.

Furthermore, some embodiments of the invention may include alternativetechniques to build systems based on integrated 3D devices includingtechniques and methods to construct 3D IC based systems that communicatewith other 3DIC based systems. Some embodiments of the invention mayenable system solutions with far less power consumption andintercommunication abilities at lower power than prior art. Thesesystems may be called ‘Internet of Things”, or IoT, systems, wherein thesystem enabler is a 3DIC device which may provide at least threefunctions: a sensing capability, a digital and signal processingcapability, and communication capability. For example, the sensingcapability may include a region or regions, layer or layers within the3DIC device which may include, for example, a MEMS accelerometer (singleor multi-axis), gas sensor, electric or magnetic field sensor,microphone or sound sensing (air pressure changes), image sensor of oneor many wavelengths (for example, as disclosed in at least U.S. Pat.Nos. 8,283,215 and 8,163,581, incorporated herein by reference),chemical sensing, gyroscopes, resonant structures, cantileverstructures, ultrasonic transducers (capacitive & piezoelectric). Digitaland signal processing capability may include a region or regions, layeror layers within the 3D IC device which may include, for example, amicroprocessor, digital signal processor, micro-controller, FPGA, andother digital land/or analog logic circuits, devices, and subsystems.Communication capability, such as communication from at least one 3D ICof IoT system to another, or to a host controller/nexus node, mayinclude a region or regions, layer or layers within the 3D IC devicewhich may include, for example, an RF circuit and antenna or antennasfor wireless communication which might utilize standard wirelesscommunication protocols such as G4, WiFi or Bluetooth, I/O buffers andeither mechanical bond pads/wires and/or optical devices/transistors foroptical communication, transmitters, receivers, codecs, DACs, digital oranalog filters, modulators.

Energy harvesting, device cooling and other capabilities may also beincluded in the system. The 3DIC inventions disclosed herein and in theincorporated referenced documents enable the IoT system to closelyintegrate different crystal devices, for example a layer or layers ofdevices/transistors formed on and/or within mono or poly crystallinesilicon combined with a layer or layers of devices/transistors formed onand/or within Ge, or a layer of layers of GaAs, InP, differing siliconcrystal orientations, and so on. For example, incorporating the 3D ICsemiconductor devices according to some embodiments of the invention asor within the IoT systems and mobile systems could provide superior IoTor mobile systems that could operate much more efficiently and for amuch longer time than with prior art technology. The 3D IC technologyherein disclosed provides a most efficient path for heterogeneousintegration with very effective integration reducing cost and operatingpower with the ability to support redundancy for long field life andother advantages which could make such an IoT System commerciallysuccessful.

Alignment is a basic step in semiconductor processing. For most cases itis part of the overall process flow that every successive layer ispatterned when it is aligned to the layer below it. These alignmentscould all be done to one common alignment mark, or to some otheralignment mark or marks that are embedded in a layer underneath. Intoday's equipment such alignment would be precise to below a fewnanometers and better than 40 nm or better than 20 nm and even betterthan 10 nm. In general such alignment could be observed by comparing twodevices processed using the same mask set. If two layers in one devicemaintain their relative relationship in both devices—to fewnanometers—it is clear indication that these layers are aligned each tothe other. This could be achieved by either aligning to the samealignment mark (sometimes called a zero mark alignment scheme), or onelayer is using an alignment mark embedded in the other layer (sometimescalled a direct alignment), or using different alignment marks of layersthat are aligned to each other (sometimes called an indirect alignment).

In this document, the connection made between layers of, generally,single crystal, transistors, which may be variously named for example asthermal contacts and vias, Thru Layer Via (TLV), TSV (Thru Silicon Via),may be made and include electrically and thermally conducting materialor may be made and include an electrically non-conducting but thermallyconducting material or materials. A device or method may includeformation of both of these types of connections, or just one type. Byvarying the size, number, composition, placement, shape, or depth ofthese connection structures, the coefficient of thermal expansionexhibited by a layer or layers may be tailored to a desired value. Forexample, the coefficient of thermal expansion of the second layer oftransistors may be tailored to substantially match the coefficient ofthermal expansion of the first layer, or base layer of transistors,which may include its (first layer) interconnect layers.

Base wafers or substrates, or acceptor wafers or substrates, or targetwafers substrates herein may be substantially comprised of a crystallinematerial, for example, mono-crystalline silicon or germanium, or may bean engineered substrate/wafer such as, for example, an SOI (Silicon onInsulator) wafer or GeOI (Germanium on Insulator) substrate. Similarly,donor wafers herein may be substantially comprised of a crystallinematerial and may include, for example, mono-crystalline silicon orgermanium, or may be an engineered substrate/wafer such as, for example,an SOI (Silicon on Insulator) wafer or GeOI (Germanium on Insulator)substrate, depending on design and process flow choices.

While mono-crystalline silicon has been mentioned as a transistormaterial in this document, other options are possible including, forexample, poly-crystalline silicon, mono-crystalline germanium,mono-crystalline III-V semiconductors, graphene, and various othersemiconductor materials with which devices, such as transistors, may beconstructed within. Moreover, thermal contacts and vias may or may notbe stacked in a substantially vertical line through multiple stacks,layers, strata of circuits. Thermal contacts and vias may includematerials such as sp2 carbon as conducting and sp3 carbon asnon-conducting of electrical current. Thermal contacts and vias mayinclude materials such as carbon nano-tubes. Thermal contacts and viasmay include materials such as, for example, copper, aluminum, tungsten,titanium, tantalum, cobalt metals and/or silicides of the metals. Firstsilicon layers or transistor channels and second silicon layers ortransistor channels may be may be substantially absent of semiconductordopants to form an undoped silicon region or layer, or doped, such as,for example, with elemental or compound species that form a p+, or p, orp−, or n+, or n, or n− silicon layer or region. A heat removal apparatusmay include an external surface from which heat transfer may take placeby methods such as air cooling, liquid cooling, or attachment to anotherheat sink or heat spreader structure. Furthermore, raised source anddrain contact structures, such as etch and epi SiGe and SiC, andimplanted S/Ds (such as C) may be utilized for strain control oftransistor channel to enhance carrier mobility and may provide contactresistance improvements. Damage from the processes may be opticallyannealed. Strain on a transistor channel to enhance carrier mobility maybe accomplished by a stressor layer or layers as well.

In this specification the terms stratum, tier or layer might be used forthe same structure and they may refer to transistors or other devicestructures (such as capacitors, resistors, inductors) that may liesubstantially in a plane format and in most cases such stratum, tier orlayer may include the interconnection layers used to interconnect thetransistors on each. In a 3D device as herein described there may atleast two such planes called tier, or stratum or layer.

In a 3D IC system stack, each layer/stratum may include a differentoperating voltage than other layers/stratum, for example, one stratummay have Vcc of 1.0 v and another may have a Vcc of 0.7 v. For example,one stratum may be designed for logic and have the appropriate Vcc forthat process/device node, and another stratum in the stack may bedesigned for analog devices, and have a different Vcc, likelysubstantially higher in value—for example, greater than 3 volts, greaterthan 5 volts, greater than 8 volts, greater than 10 volts. In a 3D ICsystem stack, each layer/stratum may include a different gate dielectricthickness than other layers/stratum. For example, one stratum mayinclude a gate dielectric thickness of 2 nm and another 10 nm. Thedefinition of dielectric thickness may include both a physicaldefinition of material thickness and an electrically ‘effective’thickness of the material, given differing permittivity of thematerials. In a 3D IC system stack, each layer/stratum may includedifferent gate stack materials than other layers/stratum. For example,one stratum may include a HKMG (High k metal gate) stack and anotherstratum may include a polycide/silicon oxide gate stack. In a 3D ICsystem stack, each layer/stratum may include a different junction depththan other layers/stratum. For example, the depth of the junctions mayinclude a FET transistor source or drain, bipolar emitter and contactjunctions, vertical device junctions, resistor or capacitor junctions,and so on. For example, one stratum may include junctions of a fullydepleted MOSFET, thus its junction depth may be defined by the thicknessof the stratum device silicon to the vertical isolation, and the otherstratum may also be fully depleted devices with a junction depth definedsimilarly, but one stratum has a thicker silicon layer than the otherwith respect to the respective edges of the vertical isolation. In a 3DIC system stack, each layer/stratum may include a different junctioncomposition and/or structure than other layers/stratum. For example, onestratum may include raised source drains that may be constructed from anetch and epitaxial deposition processing, another stratum in the stackmay have implanted and annealed junctions or may employ dopantsegregation techniques, such as those utilized to form DSS Schottkytransistors.

It should be noted that one of the design requirements for a monolithic3D IC design may be that substantially all of the stacked layers and thebase or substrate would have their respective dice lines (may be calledscribe-lines) aligned. As the base wafer or substrate is processed andmultiple circuits may be constructed on semiconductor layers thatoverlay each other, the overall device may be designed wherein eachoverlaying layer would have its respective dice lines overlying the dicelines of the layer underneath, thus at the end of processing the entirelayer stacked wafer/substrate could be diced in a single dicing step.There may be test structures in the streets between dice lines, whichoverall may be called scribe-lanes or dice-lanes. These scribe-lanes ordice-lanes may be 10 um wide, 20 um wide, 50 um wide 100 um wide, orgreater than 100 um wide depending on design choice and die singulationprocess capability. The scribe-lanes or dice-lanes may includeguard-ring structures and/or other die border structures. In amonolithic 3D design each layer test structure could be connectedthrough each of the overlying layers and then to the top surface toallow access to these ‘buried’ test structure before dicing the wafer.Accordingly the design may include these vertical connections and mayoffset the layer test structures to enable such connection. In manycases the die borders comprise a protection structure, such as, forexample, a guard-ring structure, die seal structure, ESD structure, andothers elements. Accordingly in a monolithic 3D device these structures,such as guard rings, would be designed to overlay each other and may bealigned to each other during the course of processing. The die edges maybe sealed by a process and structure such as, for example, described inrelation to FIG. 183C of incorporated U.S. Pat. No. 8,273,610, and mayinclude aspects as described in relation to FIG. 183A and 183B of samereference. One skilled in the art would recognize that the die seal canbe passive or electrically active. On each 3D stack layer, or stratum,the electronic circuits within one die, that may be circumscribed by adice-lane, may not be connected to the electronic circuits of a seconddie on that same wafer, that second die also may be circumscribed by adice-lane. Further, the dice-lane/scribe-lane of one stratum in the 3Dstack may be aligned to the dice-lane/scribe-lane of another stratum inthe 3D stack, thus providing a direct die singulation vector for the 3Dstack of strata/layers.

It will also be appreciated by persons of ordinary skill in the art thatthe invention is not limited to what has been particularly shown anddescribed hereinabove. For example, drawings or illustrations may notshow n or p wells for clarity in illustration. Moreover, transistorchannels illustrated or discussed herein may include dopedsemiconductors, but may instead include undoped semiconductor material.Further, any transferred layer or donor substrate or wafer preparationillustrated or discussed herein may include one or more undoped regionsor layers of semiconductor material. Moreover, epitaxial regrow ofsource and drains may utilize processes such as liquid phase epitaxialregrowth or solid phase epitaxial regrowth, and may utilize flash orlaser processes to freeze dopant profiles in place and may also permitnon-equilibrium enhanced activation (superactivation). Further,transferred layer or layers may have regions of STI or other transistorelements within it or on it when transferred. Rather, the scope of theinvention includes combinations and sub-combinations of the variousfeatures described hereinabove as well as modifications and variationswhich would occur to such skilled persons upon reading the foregoingdescription. Thus the invention is to be limited only by the appendedclaims.

I claim:
 1. A 3D semiconductor device, comprising: a first diecomprising first transistors and first interconnect, overlaid by asecond die comprising second transistors and second interconnect,wherein said second die comprises at least two alignment markspositioned close to said second die edge, wherein said second die has athickness of less than four microns, wherein said second die is alignedto said first die with less than 400 nm alignment error, and whereinsaid second die comprises at least two alignment marks positioned closeto said second die edge.
 2. The 3D semiconductor device according toclaim 1, wherein said first die has a first die area and said second diehas a second die area, and wherein said first die area is at least 10%larger than said second die area.
 3. The 3D semiconductor deviceaccording to claim 1, wherein said first die is sourced from a firstwafer with a diameter greater than 280 mm and said second die is sourcedfrom a second wafer with a diameter less than 240 mm.
 4. The 3Dsemiconductor device according to claim 1, further comprising: a thirddie directly overlaying said first die.
 5. The 3D semiconductor deviceaccording to claim 1, wherein said second die is a pretested.
 6. A 3Dsemiconductor device, comprising: a first die comprising firsttransistors and first interconnect, overlaid by a second die comprisingsecond transistors and second interconnect, wherein said first die has afirst die area and said second die has a second die area, wherein saidfirst die area is at least 10% larger than said second die area, whereinsaid second die has a thickness of less than four microns, wherein saidsecond die is aligned to said first die with less than 400 nm alignmenterror, and wherein said second die comprises at least two alignmentmarks positioned close to said second die edge.
 7. The 3D semiconductordevice according to claim 6, further comprising: a through second dievia having a diameter of less than 400 nm.
 8. The 3D semiconductordevice according to claim 6, further comprising: a third die directlyoverlaying said first die.
 9. The 3D semiconductor device according toclaim 6, wherein said second die is a pretested.
 10. A 3D semiconductordevice, comprising: a first die comprising first transistors and firstinterconnect, overlaid by a second die comprising second transistors andsecond interconnect, wherein said first die is sourced from a firstwafer with a diameter greater than 280 mm and said second die is sourcedfrom a second wafer with a diameter less than 240 mm, wherein saidsecond die has a thickness of less than four microns, wherein saidsecond die is aligned to said first die with less than 400 nm alignmenterror, and wherein said second die comprises at least two alignmentmarks positioned close to said second die edge.
 11. The 3D semiconductordevice according to claim 10, wherein said first die has a first diearea and said second die has a second die area, and wherein said firstdie area is at least 10% larger than said second die area.
 12. The 3Dsemiconductor device according to claim 10, further comprising: athrough second die via having a diameter of less than 400 nm.
 13. The 3Dsemiconductor device according to claim 10, further comprising: a thirddie directly overlaying said first die.
 14. The 3D semiconductor deviceaccording to claim 10, wherein said second die is a pretested.